kony wrote:
On Sun, 31 Aug 2003 05:37:03 -0500, David Maynard
wrote:


kony wrote:

On Sat, 30 Aug 2003 21:49:12 GMT, TC wrote:




/\/\/\/\
Actually .. the ducted fan is state of the art.


Nope, Gateway, Compaq and others have been using passive coolers and
ducts since the Pentium 1 days.

True. Different designs, however.


The CPU runs hotter as a result,
then and today.

Not so. It is not 'because' of the ducted design. It because their design goal,
regardless of the chosen cooling method, is proper operation within the
temperature specs and not 'the coolest we can get it'.


The issue is not one of achieving "the coolest we can get it", but
rather noise/heat ratio, that a duct impedes exhaust, making the rear
fan noiser at the same exhaust flow rate. To keep the CPU at the same
(high) operating temp as in the Dell ducted system, a good active
cooler's fan can run at low enough RPM, low enough turbulence, that
what litte noise it creates, being buffered by the enclosure, is less
audible than the increase in ducted exhaust fan noise. Running the
rear fan at higher RPM is necessitated by the duct, else there is more
heat buildup in the system.

Nice theory but not true. Case temp is cooler because the heat is directly
exhausted rather than circulated. You also fail to take into account that the
Dell motherboard is designed with the CPU socket located to minimize duct air
impedance.

The total system heat generation can be considered constant so the
total airflow through the system must also remain the same else the
Dell system runs hotter in more areas than just the CPU.

Directly exhausting the heat requires less airflow than first mixing it then
exhausting it. Plus it results in cooler air into the heatsink because the case
air is cooler: not being first preheated with the heatsink exhaust.

Lower air
intake into the system will then result in hotter air entering the
heatsink.

There isn't necessarily lower air intake into the system but it could be as it's
easier to cool the remaining components when you don't have the CPU heat being
vented into the case.

Proper operation within the temperature spec (instead of lowest
possible CPU temp) is the notion that allows using a low-RPM fan on
the heatsink instead of the noisey fans most people compare to the
Dell ducted system.

True, but no fan is still less noise than a 'low noise' fan.

If we are considering a custom-designed OEM
cooling system it has to be compared to an active cooling stategy with
similar forethought, not just a cheap/junk $5 'sink with a
tornado-speed fan on top.

No fan is still less noise than a 'low noise' fan and, with your active HSF, you
STILL need the case fan; with more airflow because it has more volume to get rid of.

Ductwork is merely cheaper than a high-quality
heatsink,

Again, not necessarily so. Depends on the overall design.


There are a lot of variables involved with design, production, parts,
but in general a high-volume production piece of plastic should be
less costly than a second fan and more elaborate heatsink.

It's your assumption than an active heatsink is necessarily "more elaborate" for
the same cooling that I dispute.

There can
be exceptions but practically we can only consider the ducted systems
being used by OEMs, not theorectical, nonexistant systems. A ducted
cooling system does tend to be the best noise/heat ratio if there are
budget constraints, at least for an OEM who can buy in bulk.

It's also the best technical noise/heat solution between the two regardless of
cost. It's simply a more efficient use of the airflow.

In other words, it can be the best budget-optimized solution for an
OEM, but optimizing as much as possible for cooling or noise, a ducted
passive 'sink cooling system cannot attain as low a noise/heat ratio.

I have no idea what makes you think that simply recirculating hot CPU air inside
the case, rather than expelling it, is 'better'.

Ducting CPU heat out is inherently a better cooling/noise solution.

Combining the two strategies, having a duct AND an active cooler,
would be the choice for lowest temps but again the duct necessitates
an increase in noise else *something* will run hotter, and of course
it will tend to be the most expensive alternative.

You simply refuse to recognize the benefit of expelling the heat directly rather
than first mixing it with case air and then having to expel the entire case
volume to remove it. You don't NEED the same airflow to remove the heat if it
goes directly out.

Not to mention one can use larger, quieter, fans on the rear mount than can be
shoved into the socket footprint.

which would keep the CPU cooler AND be as quiet.

Simply not possible. HSF assembly gets it's air from and discharges it's hot air
into the case, which then needs to be ventilated more than if that hot air were
immediately expelled (as it is in the ducted design). The result is more fans
(or fan speeds) and more noise for the equivalent cooling.


It is possible with a high-quality active cooler.

I don't care HOW 'quality' your active cooler is; it's still dissipating the CPU
heat INTO the case and not OUT of the case. And after you've dumped the CPU heat
into the case with an active HSF you STILL have to have a case fan to expel it.

Even though some
heated air is recirculated the primary source of audible noise in an
optimized configuration is the rear fan, which is less efficient with
a duct on it.

You have to expel the heat sooner or later and it takes less airflow if the CPU
heat is vented directly instead of having to expel the entire case volume to get
rid of it.

By optimizing both methods there might be similar
noise/heat ratios, but then the ducted system is more dependent on
preservation of the chassis airflow model.

'Preserving' the 'chassis airflow model'? What then heck does that mean? The
chassis has to be ventilated regardless. MORE so if you dump the CPU heat into it.

The other
benefit is that these systems are being shipped, sometimes great
distances under less-than-ideal conditions, so reduced heatsink weight
as on the Dells is reducing the chance of RMA due to socket or CPU
damage.

Odds are the 'passive' (it's not really passive; the fan is just located
differently) heatsink is as massive, perhaps more, than one with the fan mounted
on it. It depends on the design if removal of the fan compensates but it isn't a
foregone conclusion.


Passive 'sinks are usually less densely populated with fins and have a
greater percentage of weight at their base, which is less leveraged
force against the socket or retention mechanism.

Whether true or not it's not a passive heatsink. The fan is just located in a
different spot.

Proper fan selection is crucial to achieve low noise on an active
heatsink, but so it was also when Dell built their ducted system.

True. The point is, by ducting the hot CPU air directly out of the case, rather
than mixing it in as a HS mounted one does, there is less work needed to cool
the system.


Possibly, not not necessarily, and work is not always directly related
to _audible_ noise. Increasing the work done by a single fan by
having it create a suction through a duct, requires higher RPM, enough
so that the fan is no longer as quiet as the audible sum of [that fan
at lower RPM & turbulence, same airflow rate without duct] + [fan on
heatsink keeping CPU at same temp].

Doesn't need the same airflow over the CPU heatsink as the heatsink is operating
with cooler case air, since it's not preheated with the exhaust from the CPU.
Plus it's venting the case in addition to whatever case cooling you'd require
when dumping CPU heat into the case.


We could argue that a highly optimized (per system) duct be used, but
it would then need be compared to an optimized active 'sink, and the
optimized duct would be even less forgiving of user modifications to
the system, which must be considered on a PC.

"Optimized" is precisely what an active HSF is not. It's the 'norm' for generic
systems because one cannot make any assumptions about the system design: I.E.
what else is in it and where anything is located. You can't count on there even
being a rear exhaust port or, if it exists, that it's located where a 'standard'
duct (that doesn't exist) would lead to, not to mention you don't know the exact
location of the socket as that is left open, within reason, to the motherboard
designer. But you CAN just slap an active HSF on it and then leave case cooling
to someone else; with the typical solution being to slap gaggles of fans
everywhere to 'cool' it.